This invention relates generally to rotating disk data storage apparatuses; and particularly to that of the hard or "fixed" magnetic disk variety. More particularly, the invention deals with an improved read circuit in such apparatus for accurately reading data on both data sectors and servo sectors of the rotating disk.
The hard magnetic disk has a multiplicity of annular tracks arranged concentrically on at least one major surface thereof. Each track is divided into sectors, with intersector gaps therebetween, and each sector is subdivided into a data sector and a servo sector. The data sectors are used for the storage of main data or user information. The servo sectors have written thereon various control data such as automatic gain control (AGC) data, track addresses, and tracking servo patterns, and have mid-sector gaps aside from the intersector gaps. Read by the data transducer of an associated disk drive, all such data, on both data sectors and servo sectors of the disk are recreated from read pulses representative of the peaks of the transducer output waveform. The gaps in the disk tracks perform an important function of enabling the disk drive to detect the servo sectors.
As heretofore constructed, a read circuit, included in the hard disk drive, has had a problem in reconstructing the main data and control data on the disk. As is customary in the magnetic disk art, the main data is so recorded on the disk that the transducer on reading it produces an output of shorter wavelength and smaller amplitude than that produced on reading the control data. It may be comtemplated to make the reference level of wave shaping comparators in the read circuit low enough to enable exact recreation of the main data. Then, since this same low reference level has so far been used also for recreating the control data, difficulties have been encountered in detecting the peaks of the transducer output waveform representative of the control data. Such difficulties have led in some cases to failures in detecting the gaps and hence the servo sectors of the disk tracks.
The problem discussed above has become all the more pronounced in cases where an AGC is coupled to the output of the transducer. The intersector gaps as well as those in the servo sectors typically to carry noise magnetizations. These noise magnetizations have been so amplified as to result in the production of wrong read pulses if the gain is so determined as to suit the smaller amplitude transducer output representative of the main data. Such noise has also found its way into the read circuit, making impossible the correct reading of the track addresses and other control data, when the threshold level is made too low for reading the control data.